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From the top of a building 100 m high, the angles of depression of the top and bottom of a tower are observed to be 45° and 60° respectively. Find the height of the tower. Also find the distance between the foot of the building and bottom of the tower.



Let CD be the building such that CD = 100 m.Let AB be the tower of he

Let CD be the building such that CD = 100 m.
Let AB be the tower of height h metre. It is given that the angles of depression of the top A and the bottom B of the lower AB are 45° and 60° respectively.
i.e.,    ∠EAC = 45° and ∠DBC = 60°
Let    BD = AE = x
In right triangle AEC, we have

tan space 45 degree space equals space CE over AE
rightwards double arrow space space space space space space 1 space equals space fraction numerator 100 minus straight h over denominator straight x end fraction
rightwards double arrow space space space space space space space straight x equals space 100 space minus space straight h space space space space space space space space space space space space space space space space space space space... left parenthesis straight i right parenthesis
In right triangle BDC, we have

tan space 60 degree space equals space CD over BD
rightwards double arrow space space square root of 3 space equals space 100 over straight x
rightwards double arrow space space straight x space equals space fraction numerator 100 over denominator square root of 3 end fraction space space space space space space space space space space space space space space space space... left parenthesis ii right parenthesis
Comparing (i) and (ii), we get

100 minus straight h space equals space fraction numerator 100 over denominator square root of 3 end fraction
rightwards double arrow space space space square root of 3 left parenthesis 100 minus straight h right parenthesis space equals space 100
rightwards double arrow space space space 100 square root of 3 minus square root of 3 straight h end root space equals space 100
rightwards double arrow space space square root of 3 straight h end root equals space 100 square root of 3 minus 100
rightwards double arrow space straight h space equals space fraction numerator 100 square root of 3 minus 100 over denominator square root of 3 end fraction
rightwards double arrow space space straight h space equals space fraction numerator 100 left parenthesis square root of 3 minus 1 right parenthesis over denominator square root of 3 end fraction
rightwards double arrow space space straight h space equals space fraction numerator 100 left parenthesis 17.32 minus 1 right parenthesis over denominator 1.732 end fraction
space space space space space space space equals space fraction numerator 100 straight x space 0.732 over denominator 1.732 end fraction equals fraction numerator 73.2 over denominator 1.732 end fraction equals 42.26 space straight m

Hence,Height of tower (AB) = 42.26 m.

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At a point on level ground, the angle of elevation of a vertical tower is found to be such that its tangent is 5/12. On walking 192 metres towards the tower, the tangents of the angle is found to be 3/4. Find the height of the tower.

Let AB be the tower of height lim.D and C are points on the level ground such that distance between them are 192 mts. Let the angles of elevation of a vertical tower from points D and C be α and β respectively.


Let AB be the tower of height lim.D and C are points on the level gro

i.e.,    ∠ACB = β
and    ∠ADB = α
Let    BC = x metres
In right triangle ABC, we have

tan space straight beta space equals space AB over BC
rightwards double arrow space space space tan space straight beta space equals space straight h over straight x
rightwards double arrow space space space 3 over 4 space equals space straight h over straight x
rightwards double arrow space space space space 3 straight x space equals space 4 straight h
rightwards double arrow space space space space straight x space equals space fraction numerator 4 straight h over denominator 3 end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis ii right parenthesis
In right triangle ABD, we have

tan space straight alpha space equals space AB over BD
rightwards double arrow space space tan space straight alpha space equals space fraction numerator straight h over denominator straight x plus 192 end fraction
rightwards double arrow space space 5 left parenthesis straight x plus 192 right parenthesis space equals space 12 straight h
rightwards double arrow space space 5 straight x space plus space 960 space equals space 12 straight h
rightwards double arrow space space 5 straight x space equals space 12 straight h space minus space 960
rightwards double arrow space space straight x space equals space fraction numerator 12 straight h minus 960 over denominator 5 end fraction space space space space space space space space space space space space... left parenthesis ii right parenthesis
Comparing (i) and (ii), we get

fraction numerator 4 straight h over denominator 3 end fraction equals fraction numerator 12 straight h minus 960 over denominator 5 end fraction
rightwards double arrow space space 20 straight h space equals space 3 space left parenthesis 12 straight h space minus space 960 right parenthesis
rightwards double arrow space space 20 straight h space equals space 36 straight h space equals space minus 2880
rightwards double arrow space space minus 16 straight h space equals space minus 2880
rightwards double arrow space space space space space space straight h space equals space 180 space straight m
Hence, the height of the tower be 180 mts.



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The horizontal distance between two towers is 140 m. The angles of depression of the first tower, when seen from the top of the second tower is 30°. If the height of the first tower is 60 m. Find the height of the second tower.

AD and BE are two towers. The angle of depression of 1st tower (AD), when seen from the top of 2nd tower (BE) is 30°.
i.e.,    ∠CDE = 30°.
It is given that
AD = 60 m
and    AB = CD = 140 m.


AD and BE are two towers. The angle of depression of 1st tower (AD),

Let height of 2nd tower BE be h metres.
In right triangle CDE, we have


AD and BE are two towers. The angle of depression of 1st tower (AD),
Hence, the height of the second tower is 140.83 m.

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A boy standing on a horizontal plane finds a bird flying at a distance of 100 m from him at an elevation of 30°. A girl standing finds the angle of elevation of the same bird to be 45°. Both the boy and the girl are on opposite sides of the bird. Find the distance of bird from the girl.  


Let A be the position of boy D, be the position of girl and F be the position of kite, such that AF - 100 m; CD = 20 m; ∠BAF = 30° and ∠EDF = 45°
In right triangle ABF, we have

sin space 30 degree space equals space BF over AF
rightwards double arrow space space 1 half equals fraction numerator BE plus EF over denominator 100 end fraction
rightwards double arrow space space space 1 half equals fraction numerator 20 plus EF over denominator 100 end fraction space space space space left square bracket therefore space BE space equals space CD space equals space 20 straight m right square bracket

rightwards double arrow space space 2 left parenthesis 20 space plus space EF right parenthesis space equals space 100
rightwards double arrow space space 40 space plus space 2 space EF space equals space 100
rightwards double arrow space space space 2 space EF space equals space 60
rightwards double arrow space space EF space equals space 30 space straight m

Let DF be the length of the second kite.
Now, in right triangle DEF, we have

sin space 45 degree space equals space EF over DF
rightwards double arrow space space fraction numerator 1 over denominator square root of 2 end fraction equals 30 over DF
rightwards double arrow space space space space DF space equals space 30 square root of 2 straight m

Hence, the length of te string = 30 square root of 2 straight m.
Hence, the usual speed of the aircraft be x km/hr = 750 km/hr.

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A man is standing on the deck of a ship, which is 10 m above water level. He observes the angle of elevation of the top of a hill as 60° and the angle of depression of the base of the hill as 30°. Calculate the distance of the hill from the ship and the height of the hill.

Let C be position of the man. AB be the water level, and BH be the hill. The angles of elevation of the top and depression of foot from the deck of the ship be 60° and 30° respectively.
i.e., ∠DCH = 60° and ∠BCD = 30°


Let C be position of the man. AB be the water level, and BH be the hi

Let    HD = x m
In right triangle CDH, we have

tan space 60 degree equals HD over CD
rightwards double arrow space space square root of 3 space equals space straight x over CD
rightwards double arrow space space CD space equals space fraction numerator straight x over denominator square root of 3 end fraction space space space space space space space space space space space space space space space... left parenthesis straight i right parenthesis
In right triangle CDB, we have

tan space 30 degree space equals space BD over CD
rightwards double arrow space space fraction numerator 1 over denominator square root of 3 end fraction equals 10 over CD
rightwards double arrow space space space CD space equals space 10 square root of 3 space space space space space space space space space space space space... left parenthesis ii right parenthesis
Hence, distance of the ship from the hill equals 10 square root of 3 space straight m.
Comparing (i) and (ii), we get

fraction numerator straight x over denominator square root of 3 end fraction equals 10 square root of 3 space straight m
rightwards double arrow space space straight x space equals space 10 square root of 3 space straight m space straight x space square root of 3 space equals space 30 space straight m.

Now, total height of the hill
= BD + DH = 10 + x
= 10 + 30 = 40 m
Hence, height of the hill = 40 m.

 

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